1. Field of the Invention
The present invention relates to a plasma processor for generating plasma by electron cyclotron resonance (ECR).
2. Description of the Related Art
The plasma processor is structured to generate plasma by vacuum discharge in a processing chamber in which processing gas exists and to provide a predetermined processing to a processing object by use of plasma. This type of the plasma processor has been widely used in sputtering, ashing, CVD, or etching in a semiconductor manufacturing process.
As a typical plasma processor, there is used a pair of parallel plate electrodes as plasma generating means. This type of plasma processor is used under relatively high gas pressure of e.g., several hundreds nm Torr in view of an electrode structure. Due to this, an active material such as an ion material in plasma collides with the electrode, so that the electrode is sputtered, and impurity materials are generated from the electrode. For this reason, such a plasma processor has a problem with maintaining purity. Also, in such a plasma processor, there is difficulty in satisfying the recent requirement of a fine structure processing of half micron or more. In order to solve this problem, there has conventionally been disclosed an ECR plasma processor for generating plasma by use of electron cyclotron resonance under higher vacuum of several nm Torr.
In the conventional ECR plasma processor, a microwave of 2.45 GHz is normally introduced into a processing chamber, a magnetic field of 875 gausses is also applied to the processing chamber, and process gas is changed to plasma even under high vacuum of several nm Torr as a result of the electron cyclotron resonance. As a result, a rate of ionization can be improved and plasma having a high density can be obtained.
However, in the above conventional ECR plasma processor, since the microwave of 2.45 GHz is used, it is required that a predetermined physical relation be added to induce electron cyclotron resonance in such a microwave. Due to this, the magnetic field of 875 gausses must be applied to the chamber. However, in a case that etching process is provided to a semiconductor wafer in accordance with a fine pattern having a predetermined shape in a state that such a strong magnetic field is applied, plasma is easily unevenly distributed due to the strong magnetic field. Then, a charge-up phenomenon partially occurs in the semiconductor wafer by the uneven distribution of plasma, and deformation is generated in the etching shape by the charge-up phenomenon. As a result, the fine processing with high accuracy cannot be performed. Also, there is difficulty in forming the magnetic field having a uniform intensity for performing the fine processing with high accuracy.